Numerous surgical procedures are known wherein connective tissue damaged due to an accident or a disease is repaired and/or replaced. In some of such procedures, tunnels are drilled into a bone, and tissue grafts or artificial grafts are inserted into these tunnels. In the reconstruction of an anterior cruciate ligament (ACL) or a posterior cruciate ligament (PCL), for example, either a soft tissue graft or a bone-tendon-bone graft is fixed to the tunnels drilled into ends of femora and tibiae. In most cases the graft is fixed into a drilled tunnel by a screw, which is typically screwed between the graft and the drilled tunnel, pressing and locking the graft against the wall of the drilled tunnel.
Conventionally, the screws fixing the graft have been manufactured from biostable materials, such as metal. Increasingly often, however, such screws are manufactured from materials that are absorbed into the body, i.e. biodegradable materials. The use of such screws in surgical procedures is constantly on the increase since they provide a considerable advantage over conventional implants manufactured from metal: they do not have to be removed from the body after the operated tissue has healed. This enables an operation to remove the implant to be avoided, which is naturally advantageous in terms of patient satisfaction and resource load as well as costs.
Screws manufactured from biodegradable materials allow for less angular force than metallic screws do. In order to prevent a biodegradable screw from breaking down while being screwed into a drilled tunnel, the mouth part of the drilled tunnel is enlarged e.g. by bevelling the edge of the mouth part. Different instruments have been developed for the purpose, and they are usually called notchers. Hereinafter, in the present application the term instrument is used for referring to instruments used for shaping a mouth part of a drilled tunnel.
Instruments are known which are used for shaping a mouth part by turning the instrument at the mouth part of a drilled tunnel. Such an instrument includes several blades arranged radially around the shaft of the instrument. When the operator turns the instrument at the mouth of the drilled tunnel by a wrist movement, the turning angle being about 90° at its largest, the blades shape the surfaces surrounding the instrument everywhere. Such a shaped surface thus extends 360° around the instrument.
Operators usually wish to perform an operation such that a graft is first inserted into a drilled tunnel and the mouth part of the drilled tunnel is shaped using an instrument only thereafter. The instrument is then inserted into the mouth part of the drilled tunnel, between the wall of the drilled tunnel and the graft. The mouth part of the drilled tunnel now being shaped, the blades may damage the graft. The problem is particularly apparent when a soft tissue graft is used. The blades may damage the graft even to the extent that it no longer can be used in the operation but has to be replaced by a new one.